Rheostat device



Filed Nov. 12, 1941 3 Sheets-Sheet l IN VEN TUR.

o. s DH MYM 5.0m n V! R. ,h HQ V.. B u fw Sept 21, 1943. H. B. SHAPIRO 2,329,949

RHEOSTAT DEVICE l v v Filed Nov. 12, 1941 5 Sheets-Sheet 2 INVENTOR:

n Z2/f E S iro 65 BY y @0 A T T ORNEY.'

Sept 21, 1943 H. B. sHAPxRo 2,329,949

RHEOS'IA'I DEVICE Filed Nov. 12, 1941 5 Sheets-Sheet 3 FIGJI.

IN VEN TOR.

HARRrsHAP/Ro. BY WMM ATTORNEYS.

A rheostat wall grip member;

Patented Sept. 21, 1943 RHEOSTAT DEVICE Harry B. Shapiro, Cleveland, Ohio, assignor to Sonotone Corporation, Elmsford, N. Y., a corporation o! New York l Application November 12, 1941, Serial No. A418,856

13 Claims. (Cl. 2011-55) This application is a continuation-in-part of` the application Serial No. 303,563, filed November 9, 1939.

This invention relates to rheostat devices and more particularly to rheostat or potentiometer devices oi the type generally used in radio receivers or the like.

Among the objects of the invention is anovel rheostat device oi the foregoing type which'v is composed of` a lesser number of parts, occupies much less space than the best prior art devices of this type, and has various other advantages thereover. v

A distinct phase ofthe invention is a combination of such rheostat with circuit switching means which are abruptly actuated between a circuit opening and a circuit closing position incidental to the actuation oi the rheostat in respense to an adjustment of the rheostat to a certain operating position.

'I'he foregoing and other objects of the invention will 4be best understood'irom the following description of exempliiications thereof, reference being had to the accompanying drawings wherein Fig. 1 is a cross-sectional view of a rheostat device exempliiying the invention along line l-I of F18. 2: I

Fig. 2 is a top view ot the casing portion of the device with the .elements mounted therein;

Fig.3isaviewsimilarto1*ig. lalonglineI-S oi Fig. 2; v

Fig. 4 is an exploded perspective view of the device, some of its parts being omitted;

Fig. 5 is a top view illustrating a combination rheostat and switching device .of the invention utilizing arheostat device o! the type shown Figs. 1 to 3; l

Fig.6isaviewalonglineI-lofrig.5;

Ilig. 7is aviewalonglinel-l otFig.5;

Figaisaviewsimilartorlmshowingthe -switch in the closed position Just as it is about to be opened by a further clockwise turn o! the Fig. 9 is a view similar to Fig. 'l with the switch blade inthe closed position;

Fig. 10 is a iront elevational view illustrating the mounting ofthe rheostat .and switching unit showninFigatos; and

Figs. 11 to 13 are side elevational views illustrating diilerent ways oi moiming the rheostat device.

The rheostat device oi Figs. 1 to 4 exempliiying the invention was invented for use as a part ot Aa wearable electron-tube hearing-aid amplifier such as a synthetic resin. which is amxed to the' unit having overall dimensions oi' only about 5 x 21/2 x inches, small enough to tit into a vest pocket of a person, such as described in my copending application Serial No. 418,857, filed'November 12, 1941, as a continuation-impart of my application Serial No. 294,649, filed September 13, 1939. v

Referring to Figs. 1 to 4, the rheostat exemplifying the invention has the form of an extremely flat tiny structure composed of two facing wall members forming a circular casing i6 and a cover wall Il which are revolvably joined to each other. 'Ihe casing l0 in which all the operating parts are housed has an outer diameter of only .750 inch and its overall height is only .145 inch. In the form here shown, the casing In, which serves as the supporting wall member, is made of metal and the cover Il, which serves as the rotary wall member, is made of insulating material, such as a synthetic resin. The cooperating facing surfaces of the casing le and the cover l I are designed to interilt and prevent dust, dirt or other'ioreign matter from entering into the interior oi the casing, while permitting revolvable motion between the casing and the cover. In the `iform here shown, this is accompllshed by providing the cover Il with aclrcular groove I3 and a central hole Il overlapping and iitting over the circular rim I5 and the central vre-entrant Vcylindrical bushing portion it of the casing which bound the annular casing space from which foreign matter must be kept away.

The metallic bottom wall of the casing Il is covered by a thin insulating washer i'l, or paper, for instance. A shoulder-bushing Il of insulating material is placed around the re-entrant bushing it of the casing above the insulating washer Il. Around the lower flange of. the shudder-bushing AIl, above the underlying periphery of the insulating washer IL'is'mounted a fiat ring-shaped resistance element It'having a substantially rigid body 'of insulating material.

bottom wall oi the casing Il by means o! two rivets Il extending through holes of the casing Il and clamped thereto. Although wire-wound resistance elements maybe used in the unit here shown. the long arcuate portion oi the ring-like resistance element I! extending between the two rivetsliscoa'tedwltharesistanceiilmzland.

cach rivet 2l has a rivet head 22 which makes a good electric contact with the underlying end Portions of thearcuate resistanceiilm 2i soas to form an external terminal connection thereto.

millating bushings Il lld 311 insulating strip Il serve as terminals for its resistance film 2|.

To the underside of the central portion of the cover is clamped, as by means of two rivets 2B, a resiliently pressing slider arm 28 provided with a stud-like contact member 29 mounted in a hole of the arm 28 and having a rounded surface which is pressed by the slider arm 28 against the resistance iilm 2| of the resistance element I9 while it is moved over its arcuate surface between the stop pins of its two rivet terminals The cover II with its slider arm 28 is revolvably joined to the casing I0, as by a screw 32 engaging the inner threaded surface of the central bushing I6 of the casing I8, the at head of the screw 32 fitting -ush a. suitable depression in the outer surface of the cqver I A spring washer 34 provided with bent springy ripple portions and a spacer washer 35 are mounted between the shoulder of the bushing IB and the overlying portion of the cover II to hold the cover in its revolvable operating position shown in Figs. l to 3. Interposed between the spring washer 35 and the underlying portion of the shoulder-bushing I8 is a circular contact plate having a terminal arm 4I overlying the uncoated portion of the resistance element I9, extending between its two ternationfby dust, and other foreign matter. central wall portions of the rheostat'casing are I to the desired angular position, in which the conminal rivets 28, and a similar rivet 42 insulatingly mounted within a hole of the casing I8 clamps the contactplate arm to the casing and provides an insulated external terminal connection to the movable contact member of the rheostat. y

A rheostat or potentiometer constructed in the way described above may be designed to have its contact member 29 in direct sliding contact engagement with the resistance flhn 2| for varying the resistance by moving the contact member to diierent arcuate portions of the resistance film 2 I. In the form shown in the drawings, the contact plate 48 is formed of a plurality of spokes carrying a flexible contact rim 44 overlying the arcuate resistance iihn 2| and held biased at a 1 gap distance away from the lm 2| so that the sliding motion of the contact member 29 presses successive portions of the iiexible rim into contact engagement with diiierent points along the arcuate resistance film 2|. The contact rim 44 of the contact plate 4u has its outer edge stiflened by curving it into convex shape in the Way shown in Figs. 3 and 4. The spokes and the rim 44 of the contact plate 48 are designed to have a total stiinesswhich is suiiicient to keep the rim biased away from its engagement with Ithe resistance film 2 I, and the edge of the contact rim 44 is sufiiciently stiiened by the curved convex edge portion so that substantially the entire periphery of the rim exerts substantially the same restoring forces which oppose its 'being bent by the sliding contact member 29 into engagement with the resistance film 2| when the contact member 29 is ymoved along the rim. With such arrangement, the rim por-tion 44 of theA contact plate 48 is used to make variable contactwith diierent portions of the resistance film 2|, and the movable contact member 29, which is used only to press different peripheral portions of thef'contact plate portion into engagement with the resistance iilm,

may be' made of insulating material."

Underneath the outer rivet heads of the terminal rivets 20 and 42 may be clamped suitable terminal strips 41, 48 for making connections to external circuits. v

In the rheostat unit described above, the two relatively movable rheostat elements are carried by two relatively movable Wall members of the casing which encloses all operating elements of the rheostat and protects them against contamidesigned to form the revolvable junction which keeps the relatively movable rheostat elements in their proper operating positions. This a rrange.

tact arm 28 with itsl contact member 29 presses the underlying portion dpf the rim of the contact plate 40 into engagement with the desired point portion of the arcuate resistance film 2|. This establishes a connection between the terminal rivet 42, which is connected to the contact plate 40, and the desired point of the resistance film 2| which isA connected by means of its terminal rivets 2U to the associated operating circuits.

In the rheostat or volume control potentiometer device described above, the casing I0 and the cover II form thus two relatively movable substantially parallel wall members having overlapping portions oo'nfining a substantially circular interior space in which the rheostat elements are housed. One of thetwo parallel wall members, namely the casing I0, carries one 0f the rheostat elements, namely the resistor element ring I9, provided with an elongated arcuate resistance film coating 2| and held in fixed posi- 'tion on the casing by the rivets 20 which serve arm 28 with its contact projection 29 which are carried by the other wall member of the casing, namely, the cover II, and rotated thereby so as to press consecutive peripheral portions of the contact rim 44 into electrical contact engagement with the selected portions of the resistance iilm 2|. The two relatively movable parallel wall members confine the two cooperating rheostat elements in the space inclosed by the wall members and the two wall members are revolvably joined so that by rotating one wall member relatively to the other the movable contact member is electrically connected to different consecutive portions of the resistance film 2|. This arrangement makes it possible to construct a compact fully protected rheostat or potentiometer device in the form of an extremely at casing, and to utilize a laterally projecting rim portion of one of the wall members, which does not occupy any additional height, for actuating therheostat device to different points of its operating range.

Such rheostat unit may bemounted in its operating position in a variety of ways. Thus, when 'used as a volume control of a iiat wearable elec- The it may be provided with a supporting strip 50 of metal, extending from, or suitably secured, as by spot welding, to the bottom wall of the casing l0, for mounting the resistance unit in its location.

As explained above, the rheostat device of the invention was evolved in connection with the development of a vacuum tube hearing aid. In such hearing aids, it is of utmost importance to reduce to a minimum the number of controls which have to be operated by the user in order to adjust the sound output of the hearing aid and effect energization or deenergization of the hearing aid.

One phase of the present invention resides in the combination of a rheostat device of the type described in connection with Figs. 1 to 3, with foolproof reliable circuit switching means which',

are actuated abruptly ybetween a circuit closing and circuit opening position upon the actuation of the rheostat to or from a predetermined operating position. Such combined rheostat and switching' device exemplifying one form of the linvention is shown in Figs. 5 to 9.

To a supporting element 5| extending from one of the walls of a rheostat device similar to that of Figs. 1 to 3, inthe present case in the form of a strip secured, as by spot welding, to the bottom wall l0 of the rheostat device, is secured, as by rivets 54, an insulating strip 55 serving as a mounting plate for two switch Contact elements 56 and 63, respectively,`each made of a conducting resilient sheet metal strip.

Contact element 56 is made of a strip having one end aiXed to the insulating mounting plate 55 by a rivet 51 and provided with a laterally bent terminal extension 58, the other freely projecting end of the strip having an upwardly facing Acontact surface 59 and being provided with a .laterally bent guide extension 60 interfitting within a groove of the insulating mounting plate 55 so as to be guided therein when it is exed.

The other contact element 63 has a folded-overl mounting end 64 affixed to the underside of the insulating mounting strip 55 as by a rivet 65 so as to hold the freely projecting upper main portion of the contact strip 63 in a freely projecty ing position transverse to the general direction of the Contact strip over the underlying contact surface 59 of the' other contact strip 56, an intermediate portion of the contact strip 55 being provided with a terminal projection 56.

A contact blade 1| made of a relatively rigid metallic sheet member has one end pivotally held on a pivot pin member 12, one end of which is secured, as by riveting, to the insulating mounting plate 55, so that the free end of the contact blade 1| may be tilted between the full-line position shown in Fig. 5, where its free end extends V*underneath the free end of the contact strip B3,

and the closed positionin which the end of the contact blade 1| enters and makes contact with the contact surface portion .59 of the Contact strip 56 and the facing contact surface portion of the contact member 63.

A spring element bent in a plane parallel to the plane of motion of the blade member has one laterally bent arm 16 interfitting a hole in the blade member, and an oppositely bent lateral arm 11 intertting a `hole in the mounting member 55, the mounting holes of the spring 15 being arranged to cause the spring to swing the blade 1| either to the full-line open position, or

mined by the pivot pin 12 and the spring arm 11.

The movable contact wall of the rheostat device, which is utilized to adjust therheostat, and the contact blade 1| of the switch means are provided with cooperating elements designed so that with the switch blade 1| in its open position, the initial part of the motion imparted to the rheostat adjusting member from a predetermined adjusted portion will actuatethe contact blade 1| past its over-center position and cause it to snapI to the circuit closing position, whereupon the rheostat adjusting wall member is free for movement to all positions over the adjustable rheostat range, while the contact blade 1| remains stationary and unaffected in its closed position, and to bring about engagement of a portion of the wall member with a portion of the switch blade 1| while it is in the closed position to cause it to be returned with the snap action to the open position when the rheostat adjusting member II reaches the end of its adjusting movement from which it has been actuated to start the rheostat adjusting motion previously described.

In the form shown, the rheostat adjusting Wall member is providedwith a nose projection 8| arranged so as to cooperate with a cam surface projection 82 of the blade member and actuate it from the open position to the closed position when the rheostat adjusting member is started on its adjusting motion, and to cause the rheostat projection 8| to engage the cam surface projection 83 of the blade arm during the last portion of the returning motion of the rheostat and bring about the actuation of the blade member from the closed to the open position.

Fig. l0 shows how the rheostat switch unit described above in connection with Figs. 5 to 9 is mounted within a border portion of a fiat small housing 8| of a wearable vacuum tube hearing aid amplifier constituting the subject matter of to the dotted-line closed position once the spring arm 16 has moved past the center position determy copending application Serial No. 418,857 referred to hereinabove. The housing 8| has a rear wall 82 against which the mounting strip 5| of the rheostat switch combination is suitably clamped, as by screws, so that the portion of the circular periphery of the rotatable rheostat member projects through a slit 83 of the housing for enabling ready actuation of the rheostat and the switch by placing the finger against the border portion of the housing.

Rheostats of the invention, such as described above, may bemounted in its operating position in a variety of other ways.

Thus, as shown in Fig. -11, the cylindrical exterior of the casing portion of the rheostat device may be provided with a ange |52 and a threaded cylindrical surface |53 for mounting it in an opening of a supporting plate |54 by means of a nut ring |55 screwed on the threaded surface of the casing. Alternatively, as shown in Fig. 12, the shank ofthe junction screw 32 of the rheostat may be provided with a threaded extension |56 which is clamped within a hole of a supporting wall |54 by a nut |51.

If such rheostat unit is to be mounted behind a -panel for actuation by a shaft extending through a hole in the panel, in the way rheostats are usually mounted in standard radio receivers, it may be combined with a mounting bracket arranged in the Way shown in Fig. 13. The mounting bracket comprises a rectangular clamp |60 formed of a suitably bent strip of metal having at its center a threaded hole engaging an externally threaded mounting nipple |6| which fits a hole of a panel |54 and is clamped thereto by a nut |62.

A rheostat unit, such as 'shown in Figs. 1 to 4, having a casing I and a cover of a diameter substantially equal to the diameter of the casing is placed within the rectangular space of the clamp |60 and held against the yinwardly bent rear ends |64 of the clamp by a stubv shaft |65 extending through the nipple |6 The inner end of the stub shaft |65 has a key stud fitting a key hole of a key arm |61 provided with two catch lugs l'interlockingly engaging suitable depressions in the cover I I so that by rotating the shaft |65, the cover is rotated relatively to the casing I0 to actuate the rheostat. A spring washer |69 having inwardly projecting catch lugs |10 is sprung into a groove |1| of the stub shaft |65 and supplies the biasing pressure which holds the casing clamped against the inwardly bent ends |64 of the clamp. The portion of the casing engaged by the clamp ends |64 may be provided with outwardly bent projections |13 on the opposite sides of each clamp endl |64 so as to prevent rotation-of the casing when its cover is rotated by the stub shaft |65 for actuating the rheostat device.

A rheostat and mounting clamp arranged in the way shown in Fig. 13 do not occupy more spacefthan the known panel-type midget radioreceiver rheostats, and has very distinct advantages thereover because it may be quicklyy removed from its mounting position and replaced by exerting slight pressure onl the spring washer It will be apparent to those skilled in the art that the principles of the invention disclosed herein in connection with specific exemplications of the invention will suggest various other applications and modifications thereof. It is accordingly desired that in construing the breadth of the appended claims they shall not be limited to the specific exemplifcations of the invention described herein.

I claim:

1. In a rheostat device: a rotary wall member and a cooperating supporting wall member having generally parallel exterior wall surfaces forming outer boundaries of said device and interfitting facing border portions confining an interior space; one of said wall members having a circular border portion; a substantially fiat resistance element extending in al plane generally parallel to said exterior wall surfaces and connected to one of said wall members in said interior space; contact means including a slider member connected to the other wall member for establishing electrical contact engagement with different peripheral portions of said resistance element; one of said wall members having one inwardly facing junction element provided with a hole facing said interior space; one other junction element substantially confined within the exterior wall surface of the other wall member and having inwardly facing surface portions slidably engaging portions of said other wall member andv surface portions clampingly engaging the hole of said one junction element so as tb hold said wall members rotatably joined and permit one wall member to be rotated relatively to the other for actuating said slider member to adjustably establish engagement of said contact means with consecutive portions of said resistance ,element while maintaining said resistance element and said contact means enclosed in said space; said inwardly facing surface portionsof said other junction element acting as a journaling support with respect to forces exerted in directions generally parallel to the axis of said rotary movement;`the overall distance between the exterior generally parallel surfaces of said wall members being less than about half the diameter of said circular border portion; said rotary Wall member having a peripheral grip portion extending beyond the lateral boundary of the supporting wall member.

2. In a rheostat device forming part of an instrument having a flat housing small enough for comfortable wear on the body of a person: a rotary wall member and a cooperating supporting wall member having generally parallel ex- 'terior wall surfaces forming outer boundaries of said device and interfitting facing border portions conrlning an interior space; one of said wall members having a circular border portion; a substantially flat resistance element extending in a plane generally parallel to said exterior Wall surfaces and connected to one of said wall members in said interior space; contact means including a slider member connected to the other wall. member for establishing electrical contact engagement with different peripheral portions of said resistance element; one of said wall members having one inwardly facing junction element provided with a hole facing said interior space; one other junction elementI substantially conned within the exterior wall surface of the other wall member and having inwardly facing'surface portions slidably engaging portions of said other wall member and surface portions clampingly engaging the hole of said one junction element so as to hold said wall members rotatably joinedl -tions of said other junction element acting as a journaling support with respect to forces exerted in directions generally parallel to the axis of said rotary movement; the overall distance between the exterior generally parallel surfaces of 4said wall members being less than about half the diameter of said circular border portion; said supporting wall member being arranged for mounting von an interior surface portion of said housing andsaid rotary wall member having a A peripheral grip portion extending beyond the lateral boundary of the supporting wall member and arranged for gripping. through an opening in said housing.

3. In a rheostat device: a rotary wall member and a cooperating supporting wall member having generally parallel exterior wall surfaces forming outer boundaries of said device andv interfitting facing border portions confining an interior space; one of said wall members having a circular border portion; an arcuate substantially flat resistance element extending in a plane generally parallel to said exterior wall surfaces and connected to one of said wall members in said interior space; contact means including a slider member connected to the other wall member for establishing electrical contact engagement with different peripheral portions of said resistance element; one of said wall members having one inwardly facing junction element provided with a hole facing said interior space; one other junction element substantially confined within the exterior wall surface of the other wall member and having inwardly facing surface portions slidably engaging portions of said other wall member and surface portions clampingly engaging the hole of said one junction element so as to hold said wall members rotatably joinedand permit one wall member to be rotated relatively to the other for actuating said slide;` member to adjustably establish engagement of said contact means with consecutive portions of said resistance element while maintaining said resistance element and said contact means enclosed in said space; said inwardly facing surface portions of said other junction element acting as a journaling support with respect to forces exerted in directions generally parallel to the axis of said rotary movement; the overall distance between the exterior generally parallel surfaces of said wall members being less than about half the diameter of said circular border portion.

4. In a rheostat device: a rotary wall member and a cooperating supporting wall member having generally parallel exterior wall surfaces forming outer boundaries of said device and interiitting facing border portions confining an interior space; one of said wall members having a circular border portion; an arcuate substantially inwardly facing junction element provided with a hole facing said interior space; one other junction element substantially confined within the exterior wall surface of the other wall member and having inwardly facing surface portions slidably engaging portions of said other wall member and surface portions clampingly engaging the hole of said one junction element so as to hold said wall members rotatably joined and permit one Wall member to be rotated relatively to the other for actuating said slider member to adjustably establish engagement of said contact means with consecutive portions of said resistance element while maintaining said resistance element and said contact means enclosed in said space; said inwardly facing surface portions of said other junctionr element and surface portions of said circular border portion acting as journaling supports-with respect to forcesexerted in directions generally parallel to the axis of said rotary movement; the overall distance between the exterior generally parallel surfaces of said wall members being less than about half the diameter of said circular border portion.

5. In a `rheostat device: a rotary wall member and a cooperating supporting wall member having generally parallel exterior wall surfaces forming outer boundaries of said device and intertting facing border portions confining an interior space; an arcuate substantially ilat resistance element extending in a plane generally parallel to said exterior wall surfaces and connected to one of said wall members in said interior space; contact means including a slider establishing electrical contact engagement with "member connected to the other wall member for different peripheral portions of said resistance element; one of said wall members having a circular border portion and one inwardly facing junction element provided with a hole facing said interior space; one other junction element substantially confined within the exterior wall surface of the other wall member and having inwardly facing surface portions slidably engaging portions of said other wall member and surface portions clampingly engaging the hole of said one junction element so as to hold said wall members rotatively joined and permit one wall member to be rotated relatively to the other for actuating said slider member to adjustably establish engagement of said contact means with consecutive portions of said resistance element while maintaining said'resistance element and said contact means enclosed in said space; said inwardly facing surface portions of said other junction element and surface portions of said circular border portion acting as journaling supports with respect to forces exerted in directions generally parallel to the axis of said rotary movement; the overall distance between the exterior generally parallel surfaces of said wall members being less than about half the diameter of said circular border portion.

6. In a rheostat device: a rotary wall member anda cooperating supporting wall member havingv generally parallel exterior wall surfaces forming outer boundaries of said device and intertting facing border portions confining an interior space; one of said wall members having a circular` border portion; an arcuate substantially flat resistance element extending in a plane generally parallel to said exterior wall surfaces and connected to one of-said wall members in said interior space; contact means including a slider member connected to the other wall member for establishing electrical contact engagement with different peripheral portions of said resistance.

element; one of said wall members having one inwardly facing junction element provided with a hole facing said interior space; one other junction element substantially confined within the exterior wall surface of the other wall member and having inwardly facing surface portions slidably engaging portions of said other wall member and surface portions clampingly engaging the hole of said one junction element so as to hold said wall members rotatably joined and permit one wall member to be rotated relatively to the other for actuating said slider member to adjustably establish engagement of said contact means with consecutive portions of said resistance element while maintaining said resistance element and said contact means enclosed in said space; said inwardly facing surface portions of said other junction element acting as a journaling support with respect to forces exerted in directions generally parallel to the axis of said rotary movement; the overall distance between the exterior generally'parallel surfaces of said wall members being less than about half the'diameter of said circular border portion; surface portions of one of said Junction elements and surface portions of one of said wall members acting as journaling supports with respect to forces exerted in directions generally perpendicular to the axis of said rotary movement.

7. In a rheostat device: a rotary wall member and a cooperating supporting wall member having generally parallel exterior wall surfaces forming outer boundaries of said device and intertting facing border portions confining an interior space; one of said wall members having a circular border portion; an arcuate substantially fiat resistance element extending in a'V plane generally parallel to said exterior wall surfaces and connected to one of said wall members in said interior space; contact means including a slider member connected to the other wall member for establishing electrical contact engagement with different peripheral portions of said resistance element; one of said wall members having one inwardly facing junction element provided with a hole facing-said interior space; one other junction element substantially confined Within the exterior wall surface of the other wall member and having inwardly facing surface portions slidably engaging portions of said other wall member and surface portions clampingly engaging the hole of said one junction element so as to hold said wall members rotatably joined and permit one wall member to be rotated relatively to the other for actuating said slider member to adjustably establish engagement of said contact means with consecutive portions of said Vresistance element while maintaining said resistance element and l said contact means enclosed in said space; said inwardly facing surface portions of said other junction element and surface portions of said circular border portion acting as journaling supports with respect to forces exerted in directions generally parallel to the axis of said rotary movement; the overall distance between the exterior generally parallel surfaces of said wall members being less than about half the diameter of said circular border portion; surface portions of one of said junction elements and surface portions of one of said wall members acting'as journaling supports with respect to forces exerted in directions generally perpendicular to the a 's of said rotary movement.

8. in a rheostat device: a rotary wall member and a cooperating supporting wall member having generally parallel exterior wall surfaces forming outer boundaries of said device and intertting facing border portions confining an interior space; an arcuate substantially flat resistance element extending in a plane generally parallel to said exterior wall surfaces and connected to kone of said wall members in said interior space; contact means including a slider member connected to the other wall member for establishing electrical contact engagement vwith different peripheral portions of said resistance element; one of said wall members having a circular border portion and one inwardly facing junction element provided with a hole facing said interior space; one other junction element substantially confined within the exterior wall surface of the other wall member and having inwardly facing surface portions slidably engaging portions of said other wall member and surface portions clampingly engaging the hole of said one junction element so as t hold said wall members rotatably joined and permit one wall member to be rotated relatively to the other for actuating said slider member to adjustably establish engagement of said contact means with consecutive portions of said lresistance element While maintaining said resistance element and said contact means enclosed in said space; said inwardly facing surfaceportions of said other junction element and surface portions of said circular border portion acting as journaling supports with respect to forces exerted in directions generally parallel to the axis of said rotary movement; the overall distance between the exterior generally parallel surfaces .of said wall members being less than about half the diameter of said circular border portion; surface portions of one of said junction elements and surface portions of one of said wall members acting as journaling supports with respect to forces exerted in directions generally perpendicular tothe axis of said rotary movement.

9. In a rheostat device forming part of an instrument having a fiat housing small enough for comfortable'wear on the body of a person: a rotary Wall member and a cooperating supporting wall member having generally parallel exterior Wall surfaces forming outer boundaries of said device and intertting facing border portions conflning an interior space; one of said wall members having a circular border portion;

a substantially flat resistance element extending in a plane generally parallel to said exterior wall surfaces and connected to one of said wall members in said interior space; contact means including a slider member connected to the other wall member for establishing electrical contact engagement with different peripheral portions of said resistance element; one of said Wall members having one inwardly facing junction element provided with a hole facing said interior space; one other junction element substantially confined within the exterior wall surface ,of the other wall member and having inwardly facing surface portions slidably engaging portions of said other wall member and surface portions clampingly engaging the hole of said one junction element so as to hold said wall members rotatably joined and permit one wall member tov be rotated relatively to the other for actuating said slider member to adjustably establish engagement of said contact means with consecutive portions of said resistance element While maintaining said resistance element and said contact means enclosed in said space; said inwardly facing surface portions of said other junction element and surface portions of said l circular border portion acting as journaling supports with respect to forces exerted in directions generally parallel to the axis of saidvrotary movement; the overall distance between the exterior generally parallel surfaces of said wall members being less than about half the diameter of said circular border portion; said supporting wall member being arranged for mounting on an interior surface portion of said housing and said rotary wall member having a peripheral grip portion extending beyond the lateral boundary of the supporting wall member and arranged for gripping through an opening in said housing.

10. In a rheostat device forming part of an instrument having a flat housing small enough for comfortable wear on the body of a person: a rotary wall member and a cooperating supporting Wall member having generally parallel exterior wall surfaces forming outer boundaries of said device and intertting facing border portions conning anr interior space; a substantially flat resistance element extending in a plane generally parallel to said exterior wall surfaces and connected to one of said wall members in said interior space; contact means including a slider member connectedto the other wall member for establishing electrical contact engagement with different peripheral portions of said resistance element; one of said wall members having a circular border portion and one inwardly facing junction element provided with a hole facing said interior space; one other junction element substantially confined within the exterior wall surface of the other wall member and having inwardly facing surface portions slidablyngaging portions of said other wall member and surface portions clampingly engaging the hole of said one junction element so as to hold said Wall members rotatably joined and permit one wall member to be rotated relatively to the other for actuating said slider member tol adjustably establish engagement of said contact means with consecutive portions of said resistance element while maintaining said resistance element and said contact means enclosed in said space; said inwardly facing surface portions of said other junction element and surface portions of said circular border portion acting as journaling supports with respect to forces exerted in directions generally parallel to the axis of said rotary movement; the overall distance between the exterior generally parallel surfaces of'said wall members being less than about half the diameter of said circular border portion; said supporting Wall member being arranged for mounting on an interior surface portion of said housing and said rotary wall member having a peripheral grip portion extending beyond the lateral boundary of the supporting Wall member and arranged for gripping through an opening in said housing.

1l. In a rheostat device: a rotary wall member and a cooperating supporting wall member having generally .parallel exterior wall surfaces forming outer boundaries of said device and intertting facing border portionsconfining an interior space; a substantially flat resistance element extending in a plane generally parallel to said exterior Wall surfaces and connected to one of said wall members in said interior space; contact means including a slider member connected to the other wall member for establishing elec- 1trical contact engagement with different peripheral portions of siad resistance element; one of said wall members having one inwardly facing junction element provided with a hole facing said interior space; one other junction element substantially confined within the exterior wall surface of the other wall member and having inwardly facing surface portions slidably engaging portions of said other wall member and surface portions clampingly engaging the hole of said one junction element so as to hold said wall members rotatably joined and pei-mit one wall member to be rotated relatively to the other for actuating said slider member to adjustably es-v tablish engagement of said contact means with consecutive portions of said resistance element while maintaining said resistance elementand said contact means enclosed in said space; the overall distance between the exterior ygenerally parallel surfaces of said wall members being less than about half the diameter of said circular border portion: said supporting wall member having a lateral wall extension; a stationary switch contact member and movable switch contact member mounted on said lateral wall extenf sion; said movable switch contact member being interllnked with a peripheral portion of said rotan'rwallmemberandbeingsoarrangecithaton,y

moving said rotary wall member past a predetermined position said switch contact member; are

actuated from a closed position to an open position and that on moving said rotary member in opposite direction within the region of said predetermined position said switch contact members are actuated from the open position to the `closed position. l

12. In a rheostat device forming part of an instrument having a flat housing small enough for comfortable wear on the body of a person: a rotary wall member and a cooperating supporting Wall member having generally parallel exterior wall surfaces forming outer boundaries of said device and interfltting facing border portions confining an interior space; a substantially flat resistance element extending in a plane generally parallel to said exterior wall surfaces and connected to one of said wall members in said interior space; contact means including a slider member connected to the other wall member for establishing electrical contact engagement with different peripheral portions of said resistance element; one of said wall members having one inwardly facing junction element provided with a hole facing said interior space; one other junction element substantially confined within the exterior wall surface of the other wall member and having inwardly facing surface portions slidably engaging portions of said other wall member and surface portions clampingly engaging the hole of said one junction element so as to hold said wall members rotatably joined and permit one wall member to be rotated relatively to the other for actuating said slider member to adjustably establish engagement of said contact means with consecutiveportions of said resistance element while maintaining said resistance element and said contact .means enclosed in said space; the overall distance between'the exterior generally parallel surfaces ofA said wall members being less than about half the diameter of said circular border portion; said supporting wall member being arranged for mounting on an interior surface portion of said housing and said rotary wall member having a peripheral grip portion extending beyond the lateral boundary of the supporting wall member gripping through an opening in said housing; said supporting wall member having a lateral wall extension; a stationary switch contact member and movable switch contact member mounted on said lateral wall extension; said movable switch' contact member being interlinked with a peripheral portion of said rotary wall member and being so arranged that on moving said rotary wall member past a predetermined position said switch contact members are actuated from a closed position to an op'en position and that on moving said rotary member in opposite direction within the region of said predetermined position said switch contact members are actuated from the open position to the closed position; said stationary and movable switch contact members being confined to a space extending laterally from the space confined between the exterior boundaries of said rheostat device.

13. In a rheostat device as defined by claim 12, characterized by the fact that the switch contact members operate abruptly.

HARRY B. SHAPIRO.

and arranged foi 

